Superdense massive galaxies ( r _ { e } \sim 1 kpc ; M \sim 10 ^ { 11 } M _ { \sun } ) were common in the early universe ( z \gtrsim 1.5 ) .
Within some hierarchical merging scenarios , a non-negligible fraction ( 1-10 % ) of these galaxies is expected to survive since that epoch retaining their compactness and presenting old stellar populations in the present universe .
Using the NYU Value-Added Galaxy Catalog from the SDSS Data Release 6 we find only a tiny fraction of galaxies ( \sim 0.03 % ) with r _ { e } \lesssim 1.5 kpc and M _ { \star } \gtrsim 8 \times 10 ^ { 10 } M _ { \sun } in the local Universe ( z < 0.2 ) .
Surprinsingly , they are relatively young ( \sim 2 Gyr ) and metal–rich ( [ Z/H ] \sim 0.2 ) .
The consequences of these findings within the current two competing size evolution scenarios for the most massive galaxies ( ” dry ” mergers vs ” puffing up ” due to quasar activity ) are discussed .